1. Field of the Invention
The present invention relates to a sound player including a speaker apparatus and a speaker driving apparatus, and its control method. Particularly, the present invention relates to the sound player in which the speaker apparatus and the speaker driving apparatus mutually transmits and receives a speaker characteristic and electric power to control an audio signal, and its control method.
2. Description of the Related Art
Conventionally, a Motional Feedback (MFB) has been known as a technique to correct an electroacoustic characteristic of a speaker apparatus. The MFB technique feeds back a detection signal of a vibration speed in the speaker apparatus and corrects the electroacoustic characteristic based on the detection signal.
A speaker driving apparatus using the MFB easily causes oscillation due to a phase rotation of a detection signal which becomes a feedback signal. Japanese Patent Application Laid-Open No. 3-203498 discusses a speaker system that internally includes a Digital Signal Processor (DSP) which executes correction computing and a digital interface. The speaker system adds the data that correct an electroacoustic characteristic of a speaker apparatus to an input signal in advance, thereby resolving the oscillation problem of the MFB technique.
Further, conventionally, a speaker protection circuit has been known. The speaker protection circuit regulates an output electric current of an amplifier circuit to be equal or less than an allowable limit. The speaker protection circuit prevents an accident such as disconnection of wire due to heating of a voice coil when a speaker apparatus is driven in a large sound volume.
In a conventional speaker protection circuit, there is a problem of a power loss since the speaker protection circuit detects an electric current applied to a speaker by a dropped voltage of a resistor. Further, together with decrease in power efficiency of the speaker protection circuit, distortion may be caused.
Japanese Patent Application Laid-Open No. 8-172693 discusses a speaker driving circuit that detects a signal current which flows through an output resistance of the output stage of an audio amplifier circuit, and controls the sound volume of a sound volume control circuit by the detected signal electric current to regulate the amount of output electric current.
However, according to the speaker apparatus discussed in Japanese Patent Application Laid-Open No. 3-203498, power needs to be supplied to each speaker apparatus. Therefore, electric power consumption and a cost of the speaker apparatus are increased when a plurality of speaker apparatuses is arranged, for example, in a home theater system that has a 5.1 channel configuration.
Further, unlike a general sound player illustrated in FIG. 10, as illustrated in FIG. 11, according to the above conventional sound player, an output signal of a signal source needs to be input to an amplifier through a speaker apparatus, which increases a number of wirings. Furthermore, according to the conventional sound player, power has to be supplied to a correction unit, and an input and output unit inside the speaker apparatus, which increases a number of wirings of a power supply and complicates the wiring.
Still furthermore, the speaker protection circuit discussed in Japanese Patent Application Laid-Open No. 8-172693 may supply electric power exceeding maximum input electric power to the speaker apparatus when an arbitrary speaker apparatus is connected to an output of the speaker apparatus. This is because the speaker protection circuit discussed in Japanese Patent Application Laid-Open No. 8-172693 does not include a unit configured to identify maximum input electric power and a unit configured to adjust a limit of an output electric current, in the connected speaker driving circuit.